Catalytic reforming, or hydroforming, is a process in wide use by the petroleum industry for upgrading naphthas and straight run gasolines to improve the octane quality of the product. This process is generally carried out in a multi-reactor system, usually containing three or four ferrous metal reactors in series. Each reactor is provided with a ferrous metal preheater through which the feed and hydrogen are passed during the on-oil portion of an operating cycle prior to introduction into a reactor. Each reactor is also provided with one or more beds of reforming catalyst, the feed and hydrogen being introduced generally downflow into a reactor, flowing through the catalyst beds and in sequence from one reactor to the next of the series. During the on-oil portion of an operating cycle coke deposits on the catalyst; the coke deposition resulting in a decrease in the number of catalytically active sites, with a concurrent loss of catalyst activity. Consequently, as coke builds up on the catalyst surface the temperature of a given reactor is gradually increased to offset the loss of catalyst activity caused by coke build up. Inevitably it is required that the coked catalyst be taken off oil, regenerated by burning the coke from the catalyst, and the catalyst reactivated by redispersing the agglomerated metallic hydrogenation-dehydrogenation component, e.g., platinum, or platinum and iridium. On-oil reforming, as relates to the use of a given reactor, can then be resumed.
The multi reactor system through the use of ferrous metal manifolds, pipes and valving is associated on the one hand with production facilities for on-oil use and, on the other hand, with regeneration facilities for use in regeneration and reactivation of the catalyst. When the catalyst of a reactor, or reactors, must be regenerated and reactivated the reactor must be taken off-oil and connected to the regeneration facilities. In a semi-regenerative type reforming operation, to regenerate and reactivate the coked catalyst, the entire multi reactor system is shut down for regeneration and reactivation of the catalyst. The catalyst in the several reactors is then regenerated and reactivated and the unit as a whole is then returned to on-oil production. In a cyclic reforming operation, the reactors of the multi reactor system are individually swung out of line by the piping and valving arrangement used, and the catalyst regenerated and reactivated while the other reactors are maintained on-oil. A "swing reactor" temporarily replaces a reactor which is removed from the series for regeneration and reactivation of the catalyst, after which time it is put back in series. On-oil production is continuous, and the catalyst can be regenerated and reactivated without interference with production.
The earlier platinum catalysts were readily regenerated by burning the coke off the catalyst at controlled conditions in an atmosphere of oxygen, or oxygen and chlorine, at contolled flame front temperature, and the agglomerated platinum component then redispersed with relative ease by contact at elevated temperature with chlorine, generally in admixture with oxygen, to increase the rate of dispersion. However, this is not the case with the more modern iridium-containing, or iridium promoted platinum catalysts. In an oxygen atmosphere at elevated temperature the iridium component of an iridium-containing catalyst is severely agglomerated and the catalyst readily damaged. Nonetheless techniques have been developed by virtue of which iridium, or iridium in admixture with platinum, or platinum and other metal components can be redispersed to the required high surface area state.
Regeneration and reactivation of iridium-containing catalysts typically requires one or more cycles of a sequence of steps which include (i) oxidation of the catalyst in an oxidizing atmosphere in a controlled burn off of the carbon from the coked catalyst, (ii) reduction of the oxidized metallic components of the catalysts in a hydrogen atmosphere, and (iii) treatment of the catalyst by contact of same with halogen, an admixture of halogen and oxygen, or an admixture of halogen halide and oxygen, to redisperse the agglomerated iridium component or iridium-containing metallic components. Regeneration and reactivation of the catalyst results in the formation of a large amount of iron scale within the regeneration circuit of the reactor system, and the transfer of iron from the interior of the vessels and piping of the regeneration circuit onto the surface of the catalyst of the reactor. The iron scale reacts with the catalyst and suppresses the activity of the freshly activated catalyst. The migration of scale from the regeneration circuit to the beds of catalyst within the reactor is particularly troublesome at the side of the bed first contacted by the gases from the regeneration circuit, e.g., at the top of the beds in a downflow reactor. Catalyst activity depression at this location can thus be particularly severe, the scale becoming chemically bound to the surface of the catalyst.
Exclusion of the iron scale from contact with the catalyst has been achieved by a number of prior art techniques. These include dumping the catalyst from the reactor, screening off the most contaminated portion of the catalyst, and returning the uncontaminated or less contaminated catalyst to the reactor. This quite obviously is time consuming, and not only costly as a result of the lost time, but expensive due to loss of catalyst, and lost production. The installation of an on-stream filter in advance of the reactor has also been tried, but this has resulted in significant capital expenditures, as well as increased production costs due to the pressure drop within the regeneration circuit.
Current procedures required for the regeneration and reactivation of iridium-containing catalysts thus result in the formation and transfer of iron scale from the regeneration circuit to the reactors. Reactor scale migrates to the catalyst becoming chemically bound thereto to cause decreased catalyst activity. Present methods are inadequate to deal with this problem, as a result of which the catalyst suffers loss in catalyst activity despite the fact that the basic purpose of the regeneration and reactivation procedure which is employed is to restore the activity of the catalyst prior to its return to on-oil service.